1. Field of the Disclosure
Embodiments disclosed herein relate generally to epoxy resins and epoxy resin compositions. More specifically, embodiments disclosed herein relate to curable compositions and cured compositions including an epoxy resin, an amphiphilic block copolymer toughening agent, and an inorganic nanofiller.
2. Background
Epoxies resins are one of the most widely used engineering resins, and are well-known for their use in composites with high strength fibers. Epoxy resins form a glassy network, exhibit excellent resistance to corrosion and solvents, good adhesion, reasonably high glass transition temperatures, and adequate electrical properties. Unfortunately, crosslinked, glassy epoxy resins with relatively high glass transition temperatures (>100° C.) are brittle. The poor impact strength of high glass transition temperature epoxy resins limits the usage of epoxies as structural materials and in composites.
The impact strength, fracture toughness, ductility, as well as most other physical properties of crosslinked epoxy resins is controlled by the chemical structure and ratio of the epoxy resin and hardener, by any added macroscopic fillers, toughening agents, and other additives, and by the curing conditions used. For example, rubber toughening agents have been added to epoxies to improve ductility, with a corresponding decrease in stiffness. See, for example, Ratna, D., Banthia, A. K., “Rubber Toughened Epoxy,” Macromolecular Research, 2004, 12(1), pages 11-21. Macroscopic inorganic fillers may be used to compensate for the decrease in stiffness, with a corresponding decrease in ductility. The use of both macroscopic inorganic fillers and toughening agents in an epoxy resin composition, in general, results in less than optimal improvements in stiffness and ductility due to the offsetting effects on properties. Use of various toughening agents may also result in a decrease in flow and hot wet properties, the former being due to changes in rheology of the modified system.
Toughening agents used to improve fracture toughness of epoxies include linear polybutadiene-polyacrylonitrile copolymers, oligomeric polysiloxanes, and organopolysiloxane resins. See, for example, U.S. Pat. No. 5,262,507. Other toughening agents may include carboxyl terminated butadiene, polysulfide-based toughening agents, amine-terminated butadiene nitrile, and polythioethers. See, for example, U.S. Pat. Nos. 7,087,304 and 7,037,958.
Nanoparticles may be used, for example, to improve the stiffness and dimensional stability of resulting structural composites. See, for example, U.S. Patent Application Publication Nos. 20040188883, 20060293172, 20060228261, and 20050136259.
Kinloch et al. describe the use of nanosilica and ATBN or CTBN toughening agents in epoxy thermoset compositions, and the resulting impact on glass transition temperature, toughness and other properties. See, for example, “Toughening structural adhesives via nano- and micro-phase inclusions,” Kinloch, A. J.; Lee, J. H.; Taylor, A. C.; Sprenger, S.; Eger, C.; Egan, D., Journal of Adhesion (2003), 79(8-9), 867-873; “Toughening structural adhesives using nano- and micro-phase inclusions,” Kinloch, A. A.; Lee, J. H.; Taylor, A. C.; Sprenger, S.; Eger, C.; Egan, D., Proceedings of the Annual Meeting of the Adhesion Society (2004), 27th, 96-98; “The effect of silica nano particles and rubber particles on the toughness of multiphase thermosetting epoxy polymers,” Kinloch, A. J.; Mohammed, R. D.; Taylor, A. C.; Eger, C.; Sprenger, S.; Egan, D., Journal of Materials Science (2005), 40(18), 5083-5086; “Epoxy FRCS toughened with rubber and nanoparticles.” Kinloch, Anthony J.; Mohammed, Reza C.; Taylor, Ambrose D.; Sprenger, Stephan; Eger, Christian; International SAMPE Symposium and Exhibition (2005), 50 (New Horizons for Materials and Processing Technologies), 792-799; “The interlaminar toughness of carbon-fibre reinforced plastic composites using ‘hybrid-toughened’ matrices,” Kinloch, A. J.; Mohammed, R. D.; Taylor, A. C.; Sprenger, S.; Egan, D., Journal of Materials Science (2006), 41(15), 5043-5046′ and “Improving structural epoxy adhesives with SiO2 nanoparticles,” Sprenger, S.; Kinloch, A. J.; Taylor, A. C.; Lee, J. H.; Mohammed, R. D.; Egan, D., Proceedings of the Annual Meeting of the Adhesion Society (2006), 29th 232-234.
U.S. Patent Application Publication No. 20050031870 discloses a composite powder which can be used to toughen plastics. The composite powder is formed by compounding powdery rubbers with inorganic particles. The composite powder may then be blended with plastic matrices, including epoxy resins, to result in a toughened plastic.
U.S. Patent Application Publication No. 20060205856 discloses a composition comprising a thermoplastic polyester compound and sepiolite-type clay. The composition may also include 0.5 to 20 weight percent of a toughening agent and up to 1 weight percent of an epoxy.
Accordingly, there exists a need for epoxies having good ductility and good stiffness properties.